With increasing resistance and toxicity to existing anti-retroviral agents, it is imperative that inhibitors targeted at steps in the life cycle of the human immunodeficiency virus (HIV) other than protease and reverse transcriptase be developed. Integrase (IN) inhibitors have moved into clinical trials. Therefore, resistance to IN inhibitors will arise. Specifically, it is hypothesized that resistance to IN inhibitors will adversely affect the biochemistry and structure of IN and the interactions between IN and its inhibitors. Second, through synthesis of analogues derived from existing IN inhibitors, the nature of the interactions between IN and its inhibitors can be probed. Ultimately, this will lead to inhibitors of the integration reaction that enter into animal and human testing. To test these hypotheses we propose the following specific aims: 1. Select for IN inhibitor resistant HIV and map resistance mutations. 2. Determine the effects resistance mutations have on IN, HIV replication, and integration. 3. Synthesize analogues of the DCTA's and DKA's to identify compounds with improved anti-HIV activity, improved activity against IN, and improved cellular entry. 4. Map amino acids that bind inhibitors in solution. These studies will determine the mechanisms by which IN becomes resistant to inhibitors and the cost such resistance has on viral fitness. Additionally, the NMR studies will map an inhibitor-binding pocket on the HIV IN protein and identify the specific residues that interact with IN inhibitors. The long-term aim of these studies will be to obtain information critical for the rational synthesis of second generation, clinically-useful inhibitors of HIV IN with activity against both IN inhibitor-sensitive and inhibitor-resistant isolates of HIV. One HIV protein, integrase, is critical for HIV replication and thus progression to AIDS. Inhibitors of integrase are in clinical testing. Understanding how HIV becomes resistant to these compounds and how such compounds interact with integrase are fundamental to the synthesis of better anti-HIV drugs.